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From: Roman Shaposhnik <roman@zededa.com>
To: "Roger Pau Monné" <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org, Kevin Tian <kevin.tian@intel.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Jan Beulich <jbeulich@suse.com>, Paul Durrant <paul@xen.org>
Subject: Re: [Xen-devel] PCIe IOMMU ACS support
Date: Thu, 26 Mar 2020 15:03:28 -0700
Message-ID: <CAMmSBy_oX34t5388xYUxUE_jE56bpy=wKAfujZvR1-zaehDs3g@mail.gmail.com> (raw)
In-Reply-To: <20200325110533.GC28601@Air-de-Roger>

On Wed, Mar 25, 2020 at 4:05 AM Roger Pau Monné <roger.pau@citrix.com> wrote:
> Adding the PCI and IOMMU maintainers.
> On Mon, Mar 23, 2020 at 01:55:01PM -0700, Roman Shaposhnik wrote:
> > Hi!
> >
> > I was going through how Xen support PCIe IOMMU ACS and
> > all I could find is this:
> >     https://github.com/xen-project/xen/blob/master/xen/drivers/passthrough/pci.c#L608
> > which looks to me as an attempt of enabling ACS opportunistically,
> > but still proceeding forward even if it fails.
> That's correct AFAICT. Xen will try to enable some features, but will
> proceed normally if ACS is not available, or if some of the features
> are not implemented.
> Are you looking to ensure that all devices on the system have a
> certain feature enabled?

My primary objective was to get some visibility into how Xen would
prevent two PCIe devices behind a common bridge from doing p2p
transactions (thus violating VM boundaries if those devices are
assigned to different domains).

It looks like Xen simply trusts the hardware.

> Can you provide some more details about what you expect of ACS
> handling?

I was actually surprised not to see IOMMU groups in the style of what
VFIO https://www.kernel.org/doc/Documentation/vfio.txt


  reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-23 20:55 Roman Shaposhnik
2020-03-25 11:05 ` Roger Pau Monné
2020-03-26 22:03   ` Roman Shaposhnik [this message]
2020-03-27  9:12     ` Paul Durrant
2020-03-28  0:59       ` Roman Shaposhnik

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